1. Field
One or more exemplary embodiments relate to a camera, and more particularly, to a camera in which infrared ray light sources are arranged around a lens assembly.
2. Description of the Related Art
A camera having infrared ray light sources such as infrared ray (IR) light emitting diodes (LEDs) turn on the IR light sources in order to perform photographing under an environment of low luminance or an environment where there is no visible ray.
FIG. 1 is a front view of a camera 1 in which IR light sources 102 are arranged around a lens assembly 101.
Referring to FIG. 1, the IR light sources 102 form coaxial circles about the lens assembly 101. Although in FIG. 1 the IR light sources 102 are arranged in two rows, the IR light sources 102 may be arranged only in a row. In addition, the IR light sources 102 may be arranged only on a left side and a right side of the lens assembly 101 to form a rectangle, so as to correspond to a capture screen.
FIG. 2 shows a radiation characteristic of one IR LED as the IR light source.
Referring to FIG. 2, the IR LED irradiates IRs so that a direction of the 0° angle at a point “A” becomes an optical axis. Irradiation intensity in the direction of the 0° angle is 100%. Irradiation intensities at 10° angles towards left and right sides of the 0° angle are about 93%. Irradiation intensities at 20° angles towards left and right sides of the 0° angle are about 81%. Irradiation intensities at 30° angles towards left and right sides of the 0° angle are about 70%. Irradiation intensities at 40° angles towards left and right sides of the 0° angle are about 55%. Irradiation intensities at 45° angles towards left and right sides of the 0° angle are about 50%.
Here, angles at points B and C where the irradiation intensities are 50% (in FIG. 2, 45° angles in left and right directions) are referred to as half-power angles. In other regions than the half-power angle, the irradiation angle greatly decreases.
FIG. 3 is a diagram of a first-type camera 3, in which IR light sources 102a and 102b are arranged, according to the related art, and IRs irradiated from the camera 3. Referring to FIG. 3, the first-type camera 3 according to the related art and a status of irradiating IRs from the camera 3 will be described below.
The IR light sources 102a and 102b of the camera 3 of the first type may not be arranged in two rows like in FIG. 1, but in one row. Reference numeral 308 denotes a case and reference numeral 303 denotes an IR window. A barrier wall 302 prevents diffused reflection of the IR.
An image sensor 307 and a lens holder 305 are mounted on a printed circuit board (PCB) 306 for an image sensor. Reference numeral 301 denotes a lens assembly. The IR light sources 102a and 102b are mounted on a PCB 304 for IR light sources.
Photographing target areas AR1 to AR3 corresponding to a viewing angle a of the camera 3 may be classified as main irradiation areas AR1 and AR2 and an external irradiation area AR3. The main irradiation areas AR1 and AR2 are regions that do not exceed the half-power angle (β) of the IR light sources 102a and 102b. The external irradiation area AR3 is a region exceeding the half-power angle (β) of the IR light sources 102a and 102b. 
According to the camera 3 of the first type according to the related art, if the irradiation intensity of the IR light sources 102a and 102b is set to be high, the external irradiation area AR3 may be photographed so as not to be dark, but a frequency of generating a screen saturation effect may increase.
When the irradiation intensity of the IR light sources 102a and 102b is set so as not to be high, the frequency of generating the screen saturation effect decreases, but the external irradiation area AR3 is photographed dark.
FIG. 4 is a diagram of a second type camera 4, in which IR light sources 102a to 102d are arranged, according to the related art, and IRs irradiated from the camera 4.
FIG. 5 is a diagram illustrating a photographing screen 501 of a camera, the photographing screens corresponding to the photograph target areas AR1 to AR5 of FIG. 4.
Referring to FIGS. 4 and 5, the camera 4 of the second type according to the related art and a status of irradiating IRs from the camera 4 will be described below.
The IR light sources 102a to 102d of the camera 4 of the second type are arranged in two rows as shown in FIG. 1. That is, the camera 4 includes first IR light sources 102c and 102d and second IR light sources 102a and 102b. The first IR light sources 102c and 102d are arranged around the lens assembly 301. The second IR light sources 102a and 102b are arranged between the lens assembly 301 and the first IR light sources 102c and 102d. 
Reference numeral 308 denotes a case and reference numeral 303 denotes an IR window. A barrier wall 302 prevents diffused reflection of the IR.
An image sensor 307 and a lens holder 305 are mounted on a PCB 306 for an image sensor. The IR light sources 102a to 102d are mounted on a PCB 304 for IR light sources.
Photographing target areas AR1 to AR5 corresponding to a viewing angle a of the camera 4 may be classified as main irradiation areas AR1 to AR4 and an external irradiation area AR5. The main irradiation areas AR1 to AR4 are regions that do not exceed the half-power angle (β) of the first IR light sources 102c and 102d. The external irradiation area AR5 is a region exceeding the half-power angle (β) of the first IR light sources 102c and 102d. 
According to the camera 4 of the second type according to the related art, if the irradiation intensity of the IR light sources 102a to 102d is set to be high, the external irradiation area AR5 may be photographed so as not to be dark, but a frequency of generating a screen saturation effect may increase.
When the irradiation intensity of the IR light sources 102a to 102d is set so as not to be high, the frequency of generating the screen saturation effect decreases, but the external irradiation area AR4 is photographed dark.
The information in the related art described above are considered as matters that have been addressed by the inventors to derive the present inventive concept, or as matters discovered during the course of deriving the present inventive concept. As such, the information in the related art may not be simply referred to as information which was known to the general public prior to the filing of the present disclosure.